A known air-conditioning apparatus such as a multi-air-conditioning apparatus for a building causes a refrigerant to circulate between an outdoor unit being a heat source device arranged, for example, outside a structure and an indoor unit arranged inside a room in the structure. The refrigerant rejects heat or removes heat to heat or cool air, and the air makes air-conditioned space cooled or heated. One example frequently used as such a refrigerant may be a hydrofluorocarbon (HFC) refrigerant. An example that uses a natural refrigerant, such as carbon dioxide (CO2), has also been proposed.
In an air-conditioning apparatus called a chiller, a heat source device arranged outside a structure generates cooling energy or heating energy. A heat exchanger arranged inside an outdoor unit heats or cools water, antifreeze, or the like, it is conveyed to a fan coil unit, panel heater, or the like, which is an indoor unit, and cooing or heating is performed (see, for example, Patent Literature 1).
There is also an air-conditioning apparatus called a waste heat recovery chiller in which a heat source device and an indoor unit are connected by four water pipes, cooled water and heated water and the like can be simultaneously supplied to allow cooling or heating to be freely selected in the indoor unit (see, for example, Patent Literature 2).
There is also an air-conditioning apparatus in which a heat exchanger for a primary refrigerant and a secondary refrigerant is arranged in the vicinity of each indoor unit and the secondary refrigerant is conveyed to the indoor unit (see, for example, Patent Literature 3).
There is also an air-conditioning apparatus in which an outdoor unit and a branch unit having a heat exchanger are connected by two pipes and a secondary refrigerant is conveyed to an indoor unit (see, for example, Patent Literature 4).
One existing air-conditioning apparatus such as a multi-air-conditioning apparatus for a building is the one in which a refrigerant is circulated from an outdoor unit to a relay unit, a heat medium, such as water, is circulated from the relay unit to an indoor unit, and thus power for conveying the heat medium is reduced while the heat medium, such as water, is circulated to the indoor unit (see, for example, Patent Literature 5).